I've used it but there appear to be some unpublished limitations. It is most reliable if there is a car or car sized object in front of the empty space. If I pull up to where there is a curb ahead of the empty spot, it won't put up the messages that precede parking. Regardless, automatic or manual, parallel parking is trivial with this car.
I tried it once, only because I was curious, not because I wanted to begin using it for parallel parking which is very easy when driving an i3.
Parking Assist found a suitable parking space and parked without any problems other than being so slow that I would never use it when cars behind are waiting for me to park.
But beware! There have been many reports of i3 wheels being damaged when Parking Assist drags them along a curb when it tried to park too close to the curb. Apparently, Parking Assist doesn't (can't?) detect curbs but attempts to align with vehicles ahead and behind which isn't always ideal.
I've never used it- can't afford to scratch the wheels on a leased car. Anyway, from all the vehicles I've owned, only the motorcycles were easier to park.